Dynamic control of anchor carrier for dual-connectivity service

ABSTRACT

When multiple user equipment devices (UEs) are served with dual connectivity, with each UE being served by a first access node on a respective first connection according to a first RAT and all of the UE&#39;s respective first connections having a first carrier as anchor carrier for the dual connectivity, the first access node will detect that load on the first carrier is threshold high. And in response, the first access node will (i) select one or more of the UEs based on each of the selected one or more UEs being within uplink range of the first access node on a second carrier higher in frequency than the first carrier and (ii) for each selected UE, reconfigure the UE&#39;s respective first connection from having the first carrier as the anchor carrier for the dual connectivity to instead having the second carrier as the anchor carrier for dual connectivity.

BACKGROUND

A cellular wireless network typically includes a number of access nodesthat are configured to provide wireless coverage areas, such as cellsand cell sectors, in which user equipment devices (UEs) such as cellphones, tablet computers, machine-type-communication devices, trackingdevices, embedded wireless modules, and/or other wirelessly equippedcommunication devices (whether or not user operated), can operate. Eachaccess node could be coupled with a core network that providesconnectivity with various application servers and/or transport networks,such as the public switched telephone network (PSTN) and/or the Internetfor instance. With this arrangement, a UE within coverage of thecellular network could engage in air interface communication with anaccess node and could thereby communicate via the access node withvarious application servers and other entities.

Such a network could operate in accordance with a particular radioaccess technology (RAT), with communications from the access nodes toUEs defining a downlink or forward link and communications from the UEsto the access nodes defining an uplink or reverse link.

Over the years, the industry has embraced various generations of radioaccess technologies, in a continuous effort to increase available datarate and quality of service for end users. These generations have rangedfrom “1G,” which used simple analog frequency modulation to facilitatebasic voice-call service, to “4G”—such as Long Term Evolution (LTE),which now facilitates mobile broadband service using technologies suchas orthogonal frequency division multiplexing (OFDM) and multiple inputmultiple output (MIMO). And most recently, the industry is now exploringdevelopments in “5G” and particularly “5G NR” (5G New Radio), which mayuse a scalable OFDM air interface, advanced channel coding, massiveMIMO, beamforming, and/or other features, to support higher data ratesand countless applications, such as mission-critical services, enhancedmobile broadband, and massive Internet of Things (IoT).

In accordance with the RAT, each coverage area could operate on one ormore radio-frequency (RF) carriers, each of which could be frequencydivision duplex (FDD), defining separate frequency channels for downlinkand uplink communication, or time division duplex (TDD), with a singlefrequency channel multiplexed over time between downlink and uplink use.

Further, on the downlink and uplink, each carrier could be structured todefine various physical channels including time-frequency resources forcarrying information between the access node and UEs. For example, theair interface could be divided over time into frames, each divided inturn into subframes and timeslots, and the carrier bandwidth (frequencywidth of the carrier on the downlink and/or uplink) could be dividedover frequency into subcarriers, which could be grouped within eachsubframe and timeslot to define physical resource blocks (PRBs) in whichthe subcarriers can be modulated to carry data.

In addition, certain resources on the downlink and/or uplink of eachsuch carrier could be reserved for special purposes. For instance, onthe downlink, certain resources could be reserved to define a referencesignal that UEs could measure in order to determine coverage strength,other resources could be reserved to carry downlink control-planesignaling from the access node to UEs, and other resources could bereserved to carry user-plane communications from the access node to UEs.And on the uplink, certain resources could be reserved to carry uplinkcontrol-plane signaling from UEs to the access node, and other resourcescould be reserved to carry user-plane communications from UEs to theaccess node.

Overview

In example operation, when a UE enters into coverage of such a network,the UE could initially scan for and detect threshold strong coverage ofan access node on a carrier, and the UE could responsively engage insignaling with the access node to establish a Radio Resource Control(RRC) connection between the UE and the access node. Further, ifappropriate, the UE could then engage in attach signaling with acore-network controller to attach and thus register for service, and thecore-network controller could coordinate setup for the UE of one or moreuser-plane bearers, including for each bearer an access-bearer portionthat extends between the access node and a core-network gateway thatprovides connectivity with a transport network and a data-radio-bearer(DRB) portion that extends over the air between the access node and theUE.

Each such bearer could have a respective quality-of-service (QoS) classindicator (QCI) that defines certain QoS performance characteristics forthe bearer, such as whether or not the bearer has a guaranteed bit rate(GBR or non-GBR), what the packet-delay budget is for the bearer, whatthe allowed packet error rate is for the bearer, and so forth. Forinstance, one bearer that could be set up initially for the UE could bea non-GBR best-efforts bearer, perhaps a QCI 9 bearer, for carryinggeneral packet-data communications. Further, if the UE subscribes tovoice-over-packet (VOP) calling service, another bearer that could beset up initially for the UE could be a VOP signaling bearer, perhaps aQCI 5 bearer, for carrying Session Initiation Protocol (SIP) or othersuch signaling that would be used to set up or tear down VOP calls.Other examples are possible as well.

Once the UE is connected and attached, with one or more such bearersestablished, the access node could then serve the UE with packet-datacommunications.

For instance, when the core-network gateway receives packet-data fortransmission to the UE, the data could flow over an appropriate accessbearer to the access node, and the access node could buffer the data,pending transmission of the data over the associated DRB to the UE. Withthe example air-interface configuration noted above, the access nodecould then allocate downlink PRBs in an upcoming subframe for carryingat least some of the data to the UE. And in that subframe, the accessnode could transmit to the UE a scheduling directive that indicateswhich PRBs will carry the data, and the access node could transmit thedata to the UE in those PRBs.

Likewise, on the uplink, when the UE has packet-data for transmission onthe transport network, the UE could buffer the data, pendingtransmission of the data over an appropriate DRB to the access node, andthe UE could transmit to the access node a scheduling request thatcarries a buffer status report (BSR) indicating the quantity of datathat the UE has buffered for transmission. With the exampleair-interface configuration noted above, the access node could thenallocate uplink PRBs in an upcoming subframe to carry at least some ofthe data from the UE and could transmit to the UE a scheduling directiveindicating those upcoming PRBs, and the UE could accordingly transmitthe data to the access node in those PRBs. And the data could then flowover the associated access bearer through the core network for outputonto the transport network.

Further, when the UE is so served by an access node, the UE could alsoregularly monitor the strength of its coverage to help ensure that theUE is served with sufficient and/or the strongest available coverage.For instance, the UE could regularly measure reference-signal strengthfrom the access node and, when the reference signal strength becomesthreshold low could transmit a measurement report to the access node.And in response, the access node could then direct the UE to scan forcoverage of other access nodes, and if the UE finds sufficiently strongcoverage of another access node, the UE could transmit a measurementreport to the serving access node, and the serving access node couldcoordinate handover of the UE to the other access node.

In addition, while a UE is so served by an access node, other bearerscould be set up for the UE to facilitate carrying particular types oftraffic. For example, if the UE is voice capable, a VOP call might beinitiated for the UE, and the core network might responsively triggersetup for the UE of a dedicated GBR bearer, such as a QCI 1 bearer,appropriate for carrying voice traffic to and from the UE. As anotherexample, if the UE engages in packet-based gaming communication, thenetwork may set up for the UE a dedicated GBR bearer, such as a QCI 3bearer, appropriate for carrying gaming traffic to and from the UE.Other examples are possible as well.

As the industry advances from one generation of RAT to the next, issuesarise with the need for UEs to support potentially multiple RATs atonce. With the transition from 4G LTE to 5G NR, for instance, networksand UEs may be configured to support use of both technologiesconcurrently, with an arrangement referred to as EUTRA-NR DualConnectivity (EN-DC). With such an arrangement, a UE might include a 4GLTE radio and a 5G NR radio, and the 4G LTE radio could be served by a4G LTE access node (evolved Node-B (eNB)) concurrently with the 5G NRradio being served by a 5G access node (next generation Node-B (gNB)).This arrangement could help support transition from 4G LTE technology to5G NR technology and could also facilitate higher peak data rate, andpossibly lower-latency, of communication by allowing data to bemultiplexed over 4G LTE and 5G NR connections, among possibly otherbenefits.

More generally, dual connectivity could encompass connectivity on two ormore RATs concurrently, to facilitate technology transitions or forother purposes. Dual connectivity can thus be distinguished fromstandalone connectivity, where a UE is served on just one RAT, such asjust LTE for instance.

In a representative dual-connectivity arrangement, a first access nodeoperating under a first RAT could serve as a primary anchor node for thedual-connectivity service, responsible for coordinating setup andteardown of dual-connectivity service for a UE, handling core-networkcontrol-plane signaling related to the dual-connectivity service, andcontrolling handover of the UE when appropriate. Whereas, a secondaccess node operating under a second RAT could serve as a secondary nodeto provide increased data capacity for the UE. For example, with EN-DC,a 4G LTE eNB could operate as the anchor node, and a 5G NR gNB couldoperate as the secondary node.

When the UE enters into coverage of such a system, the UE couldinitially scan for and discover threshold strong coverage of a firstaccess node under a first RAT (e.g., 4G coverage, for EN-DC), and the UEcould responsively engage in signaling as discussed above to establishan RRC connection between the UE and that first access node. Further,the UE could engage in attach signaling with a core-network controllervia the first access node, and the core-network controller couldcoordinate establishment for the UE of at least one bearer as discussedabove.

The first access node could then serve the UE in a first-RAT standalonemode (i.e., under just the first RAT) with packet-data communications inthe manner described above.

Further, when starting to serve the UE or subsequently while serving theUE, the first access node could detect (e.g., encounter) a trigger fortransitioning the UE from being served with standalone connectivity bythe first access node under the first RAT to being served instead withdual connectivity by the first access node under the first RAT and asecond access node under a second RAT. By way of example, the triggercould be a determination that the UE is going to engage in a particulartype of communication that might benefit from dual-connectivity service.For instance, the trigger could be a determination that the UE is goingto engage in latency-sensitive communication or the like, which thefirst access node might learn based on setup for the UE of a bearerhaving a particular QCI value suggesting latency-sensitivity or thelike.

Operating as a master node for dual-connectivity service, the firstaccess node could then responsively engage in a process to establish forthe UE a secondary RRC connection with a second access node under asecond RAT, so that the first and second access nodes can thencooperatively provide the UE with dual-connectivity service. Forinstance, the first access node could direct the UE to scan forsecondary coverage under the second RAT and could receive in responsefrom the UE a report that the UE detected threshold strong coverage ofthe second access node. And the first access node could then coordinatesetup of dual-connectivity service with the UE being served by the firstaccess node and the second access node.

While the specifics of setting up dual connectivity may vary fromimplementation to implementation, in an example, the first access nodecould engage in signaling with the second access node, with the UE, andwith the core-network controller, to coordinate setup of thedual-connectivity service. For instance, the first access node couldengage in signaling with the UE and with the second access node toarrange for setup of a secondary connection between the UE and thesecond access node. And the first access node could engage in signalingwith the core-network controller and/or with the second access node toestablish for the UE a split-bearer arrangement so that the first accessnode could serve a portion of the UE's data communications and thesecond access node could serve another portion of the UE's datacommunications.

When considering whether to establish dual-connectivity service for aUE, the first access node may require that the UE have at least aminimum threshold quality of communication with the first accessnode—since the first access node will function as the anchor node forthe UE's dual-connectivity service. As part of this, the first accessnode may require, as a condition for setting up the dual-connectivityservice, that the UE have at least a predefined minimum threshold highlevel of uplink throughput with the first access node. The first accessnode could determine this by evaluating actual uplink data throughputfrom the UE. Alternatively, the first access node could consider whetherthe UE's most-recently reported downlink signal strength (e.g.,reference signal receive strength (RSRP)) or other reported channelquality from the first access node is at least a predefined thresholdminimum level that is deemed to correlate with likely sufficiently highuplink throughput or otherwise with sufficiently high qualitycommunication with the first access node.

If the first access node determines that the UE's quality ofcommunication with the first access node is at least predefinedthreshold high quality, then the first access node may engage inprocessing to establish dual-connectivity service for the UE in responseto the trigger for establishing such dual-connectivity service. Whereas,if the first access node determines that the UE's quality ofcommunication with the first access node is not at least the predefinedthreshold high quality, then the first access node may forgoestablishing dual-connectivity service for the UE.

Further, if dual-connectivity service gets set up for the UE, the firstaccess node may then require that the UE maintain at least a minimumthreshold quality of communication cooperatively with the first accessnode and the second access node, as a condition for maintaining thedual-connectivity service. For instance, the first access node mayrequire, as a condition for maintaining the UE's dual-connectivityservice, that the UE have at least a predefined minimum threshold levelof an uplink throughput cumulatively across the UE's first connectionwith the first access node and the UE's second connection with thesecond access node. To evaluate this, the first access node may receiveuplink-throughput reports from the second access node and may compileits own records as well, and the first access node may combine thatinformation together to establish the UE's cumulative uplink throughput(e.g., on average over a recent sliding window).

If the first access node determines that the UE's uplink throughput withdual-connectivity service is at least predefined threshold high, thenthe first access node may maintain the UE's dual-connectivityconfiguration. Whereas, if the first access node determines that theUE's uplink throughput with dual-connectivity service is below thepredefined threshold level, then the first access node may responsivelyde-configure the UE's dual connectivity service. Namely, the firstaccess node may engage in signaling to de-configure the split-bearerconfiguration that was set up for the UE and may engage in signaling torelease the second connection that was set up for the UE, thustransitioning the UE from being served with the dual connectivity backto being served with standalone connectivity by the first access node.

One technical consideration that may arise in this situation is whatcarrier the UE's first connection uses. Carriers of various frequenciesmight be available for use on the first RAT, and those carriers mightdiffer from each other in terms of their path loss and therefore interms how far from the first access node they could support sufficientlyhigh-quality UE communication with the first access node. In general,lower-frequency carriers may have lower path-loss and may thereforesupport up to more distant communications, whereas higher-frequencycarriers may have higher path-loss and may therefore have more limitedrange.

In an example system, for instance, one or more carriers might bedefined in a relatively low-frequency band, such as B25 (FDD carriers inthe range of 1850 MHz to 1915 MHz on the uplink and 1930 MHz to 1995 MHzon downlink), having relatively low path loss, whereas one or more othercarriers might be defined in a relatively high-frequency band, such asB41 (2496 MHz to 2690 MHz), having higher path loss.

If a UE's first connection with the first access node is on a firstcarrier and the UE has relatively weak coverage of the first access nodeon that carrier, then, as discussed above, the first access node maydecline to establish dual-connectivity service for the UE. Therefore,the UE may not benefit from dual-connectivity service.

Per the present disclosure, one way to help avoid this undesirableresult is for the first access node to reconfigure the UE's firstconnection from being on the first carrier to instead being on a secondcarrier that the first access node selects based on the second carrierbeing lower in frequency than the first carrier. For instance, if thefirst connection is on a B41 carrier, the first access node couldreconfigure the first connection to instead be on a B25 carrier. Doingthis may help to reduce path loss thereby improve quality of the UE'scoverage on the first connection, so that the first access node couldthen establish dual-connectivity service for the UE.

Note that the carrier at issue in this process could be the sole carrieron which the UE's first connection with the first access node isconfigured. In that case, the first access node could reconfigure thefirst connection from being on just the first carrier to being insteadon just the second carrier.

Alternatively, the carrier at issue could be a primary, anchor carrierfor carrier-aggregation service of the UE on the first connection wherethe UE is served on the first connection on the primary, anchor carrierin combination with one or more secondary component carriers. In thatcase, the first access node could reconfigure the first connection fromhaving the first carrier be the primary component carrier for thecarrier-aggregation service to instead having the second carrier be theprimary component carrier for the carrier-aggregation service.

In addition, if the first access node is serving multiple UEs that eachhave dual-connectivity service including a respective first connectionwith the first access node, a further technical issue could arise if allof the UEs' first connections are configured on the same first carrieras each other. Namely, in that scenario, the load on that first carriercould become threshold high, which could present problems withsupporting communications for some of the UEs.

Per the present disclosure, one way to help address this additionalissue is for the first access node to detect the load situation on thefirst carrier and responsively reconfigure the first connection of eachof one or more selected UEs from having the first carrier as anchorcarrier for dual-connectivity service to instead having a second carrieras anchor carrier for dual-connectivity service. Here, in contrast tothe scenario above, the second carrier could be higher in frequency thanthe first carrier; for instance, the first carrier could be a B25carrier, and the second carrier could be a B41 carrier, among otherpossibilities.

In this implementation, the first access node could select one or moreof the UEs to have their dual-connectivity anchor carrier be changedfrom the lower-frequency first carrier to the higher-frequency secondcarrier, with the selection of each such UE being based on adetermination the UE is within uplink coverage range of the first accessnode on the higher-frequency second carrier. For instance, for each UEthat has its first connection configured on the first carrier, the firstaccess node could compare a geographic location of the UE with apre-mapped uplink communication range of the first access node on thesecond carrier. And if the UE's geographic location is within thatpre-mapped uplink coverage range of the first access node, then thefirst access node could select the UE as one to have its anchor carrierfor dual connectivity reconfigured from being the first carrier toinstead being the second carrier.

Reconfiguring the anchor carrier for dual-connectivity service of eachof one or more selected UEs to be on the higher-frequency second carriercould help to reduce load on the first carrier and thereby increase thelikelihood of retaining dual-connectivity service for each other UEwhose anchor carrier for dual-connectivity service remains on the firstcarrier. Further, as the selecting of the one or more UEs is based oneach selected UE being within uplink range of the first access node onthe higher-frequency second carrier, each such selected UE may also beable to attain sufficiently high uplink throughput to also be able toretain its dual-connectivity service.

Note here as well that carrier at issue in this process could be thesole carrier on which the UE's first connection with the first accessnode is configured, or the carrier at issue could be a primary, anchorcarrier for carrier-aggregation service on the UE's first connection,with the reconfiguration being as discussed above.

These as well as other aspects, advantages, and alternatives will becomeapparent to those reading the following description, with referencewhere appropriate to the accompanying drawings. Further, it should beunderstood that the discussion in this overview and elsewhere in thisdocument is provided by way of example only and that numerous variationsare possible.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a simplified block diagram of an example network arrangementin which aspects of the present disclosure can be implemented.

FIG. 2 is a flow chart depicting an example method in accordance withthe disclosure.

FIG. 3 is another flow chart depicting an example method in accordancewith the disclosure.

FIG. 4 is a simplified block diagram of an example access node operablein accordance with the disclosure.

DETAILED DESCRIPTION

An example implementation will now be described in the context of asystem that supports 4G LTE, 5G NR, and EN-DC service. However, itshould be understood that the principles disclosed herein could extendto apply with respect to other scenarios as well, such as with respectto other RATs and other dual-connectivity configurations. Further, itshould be understood that other variations from the specificarrangements and processes described are possible. For instance, variousdescribed entities, connections, functions, and other elements could beadded, omitted, distributed, re-located, re-ordered, combined, orchanged in other ways. In addition, it should be understood thatoperations described as being performed by one or more entities could beimplemented in various ways, such as by a processor executinginstructions stored in non-transitory data storage, along withassociated circuitry or other hardware, among other possibilities.

FIG. 1 is a simplified block diagram of an example network arrangementthat supports providing wireless-packet-data service according to 4G LTEand 5G NR protocols and providing EN-DC service.

The example network arrangement is shown including a representativefirst access node 16 and a representative second access node 18. In theexample implementation, the first access node could be a 4G LTE eNB,thus providing coverage and service according to 4G LTE, and the secondaccess node could be a 5G NR gNB, thus providing coverage and serviceaccording to 5G NR. The first access node 16 and second access node 18could be co-located at a common cell site, sharing an antenna tower orother antenna structure, and sharing baseband hardware or the like, butbeing separately defined to provide discrete 4G LTE and 5G NRconnections and service.

Further, the first access node and second access node could each beconfigured to provide respective coverage and service on one or morecarriers each defining respective frequency bandwidth and air-interfaceresources for carrying communications wirelessly to/from served UEs. Inparticular, the first access node 16 is configured to provide coverageand service in accordance with 4G LTE on each of at least two carriers20, 22, and the second access node 18 is configured to provide coverageand service in accordance with 5G NR on at least one carrier 24.

Of the carriers on which the first access node provides service, carrier20 is a relatively high-frequency carrier, and carrier 22 is arelatively low-frequency carrier, i.e., carrier 20 is a higher frequencycarrier than carrier 22. For example, carrier 20 might be a B41 carrier,and carrier 22 might be a B25 carrier, among other possibilities.

In an example implementation, the respective coverage provided on eachcarrier could be divided over time into frames, subframes, timeslots,and symbol segments, and could be divided over frequency bandwidth intosubcarriers. As a result, the respective coverage could define an arrayof time-frequency resource elements, in which subcarriers can bemodulated to carry data communications.

In each subframe, these resource elements could be divided into groupsdefining the PRBs noted above, which could be allocable by theassociated access node on an as-needed basis to carry datacommunications as noted above. And certain resource elements persubframe could be reserved for other purposes, such as to carry areference signal, synchronization signals, scheduling directives,acknowledgement messages, and other control signaling.

The 4G LTE air-interface and service provided by first access node 16could differ from the 5G NR air-interface and service provided by 5G NRsecond access node 18 in various ways now known or later developed. Forexample, one may provide variable subcarrier spacing, but the other mayprovide fixed subcarrier spacing. As another example, one may havedifferent symbol time segments than the other. As still another example,one may make use of different MIMO technologies than the other. And asyet another example, with TDD carriers, one may have a flexible TDDconfiguration and the other may have a fixed TDD configuration. Otherexamples are possible as well.

As further shown, the first access node and second access node are eachconnected with a core network 26, which includes a gateway system 28 anda control node 30. In an example core network, the gateway system 28could include a serving gateway (SGW) and a packet-data network gateway(PGW) (neither shown), with the SGW having a communication interface 32with the first access node and a communication interface 34 with thesecond access node, and with the PGW providing connectivity with atransport network 36 such as the Internet or a private network. And thecontrol node 30 could be a mobility management entity (MME), which couldhave a communication interface 38 with the first access node and acommunication interface 40 with the gateway system 28 (e.g., with theSGW).

Additionally, shown possibly within coverage of the first access node 16and the second access node 18 are a number of UEs 42, each of whichcould take any of the forms noted above, among other possibilities.

As discussed above, when any such UE 42 initially enters into coverageof this network, the UE could discover coverage of the first access node16 on a first carrier, such as by scanning predefined 4G LTE carriers tofind a synchronization signal from the first access node and thendetermining that a reference signal from the first access node on thefirst carrier is strong enough to justify connecting. The UE could thenengage in random-access signaling and RRC signaling with the firstaccess node to establish a first RRC connection between the UE and thefirst access node on the first carrier. And the UE could then engage inattach signaling with the control node 30, via the first connection andthe first access node, to register for service with the network,triggering the control node 30 to coordinate setup for the UE of atleast a best-efforts bearer (e.g., QCI 9 bearer). The first access nodecould then serve the UE with standalone 4G LTE connectivity on the firstconnection.

The first carrier on which the UE is connected with the first accessnode could be the sole carrier on which the first connection is definedand could therefore be the sole carrier that carries all control-planeand user-plane communications between the UE and the first access node.

Alternatively, the first carrier could be the primary component carrierfor carrier-aggregation service defined on the first connection, withthe first access node having added one or more additional carriers eachas a secondary component carrier for the carrier-aggregation service. Inthat case, the first carrier could be the anchor for certain keycontrol-plane communications between the UE and the first access node.

Further, as discussed above, the first access node could detect atrigger for establishing EN-DC service for the UE. For instance, thefirst access node could detect bearer-setup signaling that indicatesthat the UE is going to engage in a communication that could benefitfrom EN-DC service, such signaling indicating setup for the UE of abearer having a QCI value corresponding with latency-sensitivecommunication (e.g., a QCI value indicating that the bearer is a GBRbearer, has a particular delay-budget, and/or is for voicecommunication, gaming communication, video streaming communication, orthe like). Alternatively or additionally, the first access node couldengage in deep packet inspection or the like to determine from packetdata flowing to or from the UE that the UE will be engaging in acommunication that could benefit from EN-DC service (e.g., that the UEis currently engaging in such communication and therefore will continueto engage in such communication, or that the UE is engaged in signalingto set up such communication).

The first access node could then responsively work to set up EN-DCservice for the UE. For instance, the first access node could send tothe UE an RRC message that directs the UE to scan for and report anythreshold strong coverage that the UE detects on 5G carriers. And uponreceipt of such a report from the UE specifying that the UE detectedthreshold strong coverage of coverage of second access node 18, thefirst access node could then engage in signaling with that second accessnode and with the UE to coordinate setup of a second connection betweenthe second access node and the UE. Further, the first access node couldengage in signaling with the control node 30 and/or the second accessnode 18 to coordinate splitting of the UE's bearer(s) so as to enablethe first access node and second access node to concurrently serve theUE over their respective connections with the UE.

Various split-bearer arrangements may be possible.

In one implementation, the split bearer could be established at thegateway system 28, with one bearer leg extending between the gatewaysystem and the first access node and another bearer leg extendingbetween the gateway system and the second access node. For instance,while maintaining the UE's access bearer between the first access nodeand the gateway system, the control node 30 could coordinate setup of asecondary access bearer between the second access node and the gatewaysystem. With this arrangement, communications between the UE and thefirst access node could flow over the access bearer between the firstaccess node and the gateway system, and communications between the UEand the second access node could flow over the access bearer between thesecond access node and the gateway system.

In another implementation, the split bearer could be established at thesecond access node, with the UE's access bearer extending between thegateway system and the second access node and a leg of the access bearerextending further between the second access node and the first accessnode. For instance, the control node 30 could coordinate transfer of theUE's access bearer from being between the gateway system and the firstaccess node to instead being between the gateway system and the secondaccess node, and the first access node and second access node couldcoordinate setup of the bearer leg between the first access node and thesecond access node. With this arrangement, communications between thesecond access node and the UE would flow over the access bearer betweenthe second access node and the gateway system, and communicationsbetween the first access node and the UE would flow between the firstaccess node and the second access node and likewise over the accessbearer between the second access node and the gateway system.

And in yet another implementation, the split bearer could be establishedat the first access node, with the UE's access bearer still extendingbetween the gateway system and the first access node, and with a leg ofthe bearer extending between the first access node and the second accessnode. For instance, the first access node could maintain the accessbearer between the first access node and the gateway system, and thefirst access node and second access node could coordinate setup of thebearer leg between the first access node and the second access node.With this arrangement, communications between the first access node andthe UE could flow over the access bearer between the first access nodeand the gateway system, and communications between the second accessnode and the UE could flow between the second access node and the firstaccess node and likewise over the access bearer between the first accessnode and the gateway system.

Other split-bearer arrangements might be possible as well.

With dual-connectivity service so established through this and/or othersteps, the first access node and second access node could thenconcurrently serve the UE over their respective connections with the UE,perhaps with both providing for both downlink and uplink scheduled datacommunication, or perhaps with both providing for downlink scheduleddata communication but just one of them providing for uplink scheduleddata communication.

On the downlink, for instance, some of the data destined to the UE couldbe buffered by the first access node for transmission to the UE, and thefirst access node could coordinate downlink transmission of data overthe air from the first access node to the UE as discussed above. Andother of the data destined to the UE could be buffered by the secondaccess node for transmission to the UE, and the second access node couldcoordinate downlink transmission of that data over the air from thesecond access node to the UE as discussed above.

Likewise, when the UE has data to transmit, the UE could buffer some ofthat data for transmission to the first access node as discussed aboveand the UE could buffer other of that data for transmission to thesecond access node as discussed above. Thus, the UE could send to thefirst access node a BSR indicating how much data the UE has buffered fortransmission to the first access node, and the first access node couldcoordinate uplink transmission of that data over the air from the UE tothe first access node. And the UE could send to the second access node aBSR indicating how much data the UE has buffered for transmission to thesecond access node, and the second access node could coordinate uplinktransmission of that data over the air from the UE to the second accessnode. Alternatively, the UE could limit its uplink transmission to justthe second access node.

And as noted above, the first access node could require, as a conditionfor setting up EN-DC service for the UE, that the UE have sufficientlyhigh quality communication with the first access node on the firstconnection, such as that the UE has reported sufficiently strongcoverage of the first access node and/or has sufficiently high uplinkthroughput of communication to the first access node.

Unfortunately, however, there may be situations where the UE hasrelatively weak coverage of the first access node and therefore wherethe first access node would not set up EN-DC service for the UE eventhough the first access node has detected a trigger for setting up EN-DCservice for the UE. As noted above, one such situation could be wherethe UE's first connection is on a relatively high-frequency carrier suchas carrier 20 (e.g., as sole carrier of the first connection or asprimary component carrier for carrier-aggregation service on the firstconnection), and where the UE is relatively far away from the firstaccess node. In that situation, due to the relatively high path loss onthat carrier, the UE may report relatively low RSRP from the firstaccess node. And therefore, the first access node may decline to set upEN-DC service for the UE.

In this or other situations, as discussed above, when the first accessnode detects a trigger for setting up EN-DC service for the UE, thefirst access node could responsively reconfigure the UE's firstconnection to be on a lower-frequency carrier such as carrier 22, in aneffort to improve quality of the UE's communication with the firstaccess node, so that the first access node could then set up EN-DCservice for the UE.

The process of the first access node reconfiguring the UE's firstconnection from being on the relatively high-frequency carrier 20 tobeing on the relatively low-frequency carrier 22 could initially involvethe first access node engaging in RRC signaling with the UE to confirmthat the UE is within coverage of the first access node on carrier 22,or the process may assume that the UE is within coverage of the firstaccess node on carrier 22 based on carrier 22 having lower path lossthan carrier 20.

Further, the process could involve the first access node engaging in RRCsignaling with the UE to direct the UE to hand over from being connectedwith the first access node on carrier 20 to being connected with thefirst access node on carrier 22. Alternatively, in a scenario wherecarrier 20 is configured as the primary component carrier forcarrier-aggregation service on the UE's first connection with the firstaccess node and carrier 22 is configured as one of one or more secondarycomponent carriers for carrier-aggregation service on the UE's firstconnection with the first access node, the first access node mightengage in RRC signaling with the UE to swap carriers 20 and 22, so thatcarrier 22 would become the primary component carrier for thecarrier-aggregation service and carrier 20 would become one of the oneor more secondary component carriers for the carrier-aggregationservice.

Once the first access node has so reconfigured the UE's first connectionto be on a lower-frequency carrier, the first access node could thenproceed to set up EN-DC service for the UE as discussed above, thustransitioning the UE from being served with standalone 4G LTEconnectivity by the first access node on the reconfigured firstconnection to being served instead with EN-DC by the first access nodeon the reconfigured first connection and by the second access node 18 ona second connection.

FIG. 2 is a flow chart depicting an example method for controllingconnectivity of a UE in this manner. This method could be implemented bya first access node such as access node 16 in FIG. 1, to help facilitatesetup of dual-connectivity service for the UE and/or to improve likelyquality of the UE's dual-connectivity service by improving likelyquality of the UE's anchor carrier for the dual-connectivity service.

As shown in FIG. 2, at block 44, the method includes the first accessnode serving the UE with standalone connectivity on a first connectionaccording to a first RAT, the first connection being on a first carrier.Further at block 44, the method includes, during the serving, the firstaccess node detecting a trigger for transitioning the UE from beingserved with the standalone connectivity by the first access node on thefirst connection to being served instead with dual connectivity by thefirst access node on the first connection according to the first RAT andby a second access node on a second connection according to a secondRAT.

And at block 46, the method includes, responsive to at least thedetecting, (i) the first access node reconfiguring the first connectionfrom being on the first carrier to being instead on a second carrier,based on the second carrier being lower in frequency than the firstcarrier, and (ii) after the reconfiguring (e.g., in response to thereconfiguring), the first access node transitioning the UE from beingserved with the standalone connectivity to being served with the dualconnectivity.

In line with the discussion above, the act of detecting the trigger fortransitioning the UE from being served with the standalone connectivityto being served instead with the dual connectivity could be based on aquality of service level of a communication in which the UE will beengaging, such as by detecting setup for the UE of a bearer havingpredefined threshold low packet-delay budget, among other possibilities.Thus, the act of detecting the trigger for transitioning the UE frombeing served with the standalone connectivity to being served insteadwith the dual connectivity could involve detecting that a user-planecommunication in which the UE will be engaging is latency-sensitive.

As also discussed above, in this method, the first carrier could bedefined within a first band and the second carrier could be defined in asecond band that is lower in frequency than the first band. Forinstance, the first carrier could be a B41 carrier, and the secondcarrier could be a B25 carrier.

In addition, as discussed above, the carrier at issue in this methodcould be the sole carrier on which the first connection is defined.Thus, before the reconfiguration of the first connection, the firstconnection could be on only the first carrier, and after thereconfiguration, the first connection could be on only the secondcarrier. Alternatively, the carrier at issue could be the primarycarrier for carrier-aggregation service on the first connection. Thus,before the reconfiguration, the first connection could be on the firstcarrier as a primary component carrier of carrier-aggregation, and afterthe reconfiguration, the first connection could be on the second carrieras the primary carrier of the carrier-aggregation.

Further, as discussed above, this method could additionally include,before reconfiguring the first connection, determining that the UE haspredefined threshold weak signal strength on the first connection. Andin that case, the reconfiguring of the first connection could beadditionally responsive to the determining. For instance, in response todetecting the trigger for setting up dual-connectivity service for theUE, the first access node could then consider whether the UE's RSRP onthe first carrier from the first access node is at least as low as apredefined threshold level. And if the RSRP is threshold low, then thefirst access node could proceed with the reconfiguring of the firstconnection before setting up dual connectivity for the UE. Whereas ifthe RSRP is not threshold low, then the first access node could forgoreconfiguring the first connection and could simply proceed to set upthe dual connectivity for the UE.

Still further, as discussed above, the act of transitioning the UE frombeing served with the standalone connectivity to being served insteadwith the dual connectivity could involve the first access node engagingin signaling to coordinate setup for the UE of the second connectionwith the second access node and the first access node engaging insignaling to trigger setup of a split bearer for the UE.

As additionally discussed above, when a cellular system is servingmultiple UEs with dual connectivity and all of the UE are served by acommon first access node on the same carrier as each other, a furthertechnical issue could arise. Namely, the first access node's airinterface on that carrier could become threshold heavily loaded, whichcould result in the air interface having insufficient resources foraccommodating communication needs of served UEs.

This could be a particular problem for dual-connectivity service,because each UE's first connection with the first access node is theanchor for the UE's dual-connectivity service, and because the carrierat issue is thus the anchor carrier for the UE's dual-connectivityservice. If that anchor carrier becomes threshold heavily loaded, issuescould thus arise with supporting each such UE's dual-connectivityservice.

As noted above, the present disclosure could help address this problemwhere the first access node is configured to provide service onrelatively high-frequency carrier 20 and a relatively-low frequencycarrier 22, and where the carrier at issue is the relativelylow-frequency carrier 22. That relatively low-frequency carrier 22 mightbecome threshold heavily loaded as a result of many UEs initiallyconnecting with the first access node on that carrier and/or as a resultof the first access node reconfiguring UEs' first connections from beingon the higher-frequency carrier 20 to being instead on thelower-frequency carrier 22, among other possible reasons.

Regardless of what gives rise to this situation, as noted above, thefirst access node could detect the situation and could then work addressthe situation by selectively transferring one or more UEs from eachhaving the lower-frequency carrier 22 as its anchor carrier for dualconnectivity to instead having higher-frequency carrier 20 as its anchorcarrier for dual connectivity.

The first access node could regularly monitor the load on its airinterface on lower-frequency carrier 22 and could detect when the levelof load becomes at least predefined threshold high. Here, load could bemeasured in various ways. For example, load could be measured in termsof rate of control-channel and/or shared-traffic-channel resourceoccupancy, such as rate of PRB allocation, on average over a recentsliding window, on the uplink and/or downlink. Alternatively oradditionally, load could be measured in terms of how many UEs areconnected on the carrier. Other load metrics could be possible as well.

Upon detecting that the first carrier is threshold heavily loaded, thefirst access node could then select one or more UEs to each have itsfirst connection with the first access node reconfigured from having thelower-frequency carrier 22 be the UE's anchor carrier for dualconnectivity to instead having the higher-frequency carrier 20 be theUE's anchor carrier for dual connectivity.

As noted above, the selecting of each such UE for this purpose could bebased on a determination that the UE is located within uplinkcommunication range of the first access node on the higher-frequencycarrier 20. Thus, the first access node could exclude from the selectionone or more UEs based each such UE being located too far away from thefirst access node to be able to communicate to the first access nodewith sufficiently high quality on the higher-frequency carrier 20.Whereas, the first access node could include in the selection one ormore UEs based on each such UE being located close enough to the firstaccess node to be able to communicate to the first access node with thesufficiently high quality on the higher-frequency carrier 20.

To perform this selection from among the UEs that are each connectedwith the first access node on the lower-frequency carrier 22 as anchorcarrier for dual connectivity, the first access node could determine thegeographic location of each such UE and could compare that geographiclocation with predefined coverage mapping data that defines thegeographic range of coverage of the first access node on thehigher-frequency carrier 20.

For this purpose, the first access node could determine the geographiclocation of each such UE by receiving from the UE a report of the UE'sgeographic location and/or by using any of a variety oflocation-determination techniques. And the first access node could beprovisioned with the predefined coverage mapping data that defines thegeographic range of coverage of the first access node on thehigher-frequency carrier 20.

For each UE that the first access node thus selects to have its firstconnection with the first access node reconfigured from having thelower-frequency carrier 22 be the UE's anchor carrier for dualconnectivity to instead having the higher-frequency carrier 20 be theUE's anchor carrier for dual connectivity, the first access node couldthen engage in RRC signaling with the UE to reconfigure the UE'sconnection with the first access node from being on the lower-frequencycarrier 22 to being on the higher-frequency carrier 20. Similar to theprocess discussed above, this could involve handing over the UE from onecarrier to the other and/or swapping component carrier's used forcarrier-aggregation service of the UE, among other possibilities.

Once the first access node has so reconfigured each selected UE's firstconnection have the higher-frequency carrier as anchor carrier for dualconnectivity, the UE could then continue to be served with dualconnectivity, now by the first access node on the reconfigured firstconnection and by the second access node on the second connection.

FIG. 3 is a flow chart depicting an example method for controllingconnectivity of a UE in this manner. Aspect of this method could beimplemented by one or more entities in a cellular system such as thatshown in FIG. 1, such as by first access node 16, to help maintain orfacilitate dual-connectivity service for UEs. In this method, incontrast to that discussed above, the “first carrier” could be thelower-frequency carrier 22, and the “second carrier” could be thehigher-frequency carrier 20. For instance, the first carrier could bedefined in a first frequency band (e.g., B25) and the second carriercould be defined in a second frequency band (e.g., B41) higher infrequency than the first frequency band.

As shown in FIG. 3, at block 48, the cellular system could servemultiple UEs with dual connectivity, with each UE being servedconcurrently by a first access node on a respective first connectionaccording to a first RAT and by a second access node on a respectivesecond connection according to a second RAT, and with all of the UE'srespective first connections having the same first carrier as eachother, as anchor carrier for the dual connectivity. Further, at block50, the method includes, during the serving, the first access nodedetecting that load on the first carrier is at least predefinedthreshold high. And at block 52, the method includes, responsive to thedetecting, the first access node (i) selecting one or more of the UEsbased on each selected UE being within uplink range of the first accessnode on a second carrier higher in frequency than the first carrier and(ii) for each selected UE, reconfiguring the UE's respective firstconnection from having the first carrier as the anchor carrier for thedual connectivity to instead having the second carrier as the anchorcarrier for dual connectivity.

In line with the discussion above, the first carrier could definemultiple PRBs per unit time, and the act of detecting that the load onthe first carrier is predefined threshold high could involve detectingthat a rate of allocation of the PRBs is at least predefined thresholdhigh. Alternatively, detecting the threshold high load could take otherforms.

Further, as discussed above, the act of selecting one or more of the UEsbased on each of the selected one or more UEs being within uplink rangeof the first access node on the second carrier could involve selectingthe one or more UEs based on determining that a respective geographiclocation of each of the selected one or more UEs is within a predefineduplink geographic range of the first access node on the second carrier.As such, this could involve excluding, from the selecting, one or moreother of the UEs based on the one or more other UEs each not beingwithin the predefined uplink geographic range of the first access nodeon the second carrier.

Here again, the carrier at issue could be the sole carrier on which thefirst connection is defined. Thus, for each selected UE, before thereconfiguration of the first connection, the first connection could beon only the first carrier, and after the reconfiguration, the firstconnection could be on only the second carrier.

And alternatively, the carrier at issue could be the primary carrier forcarrier-aggregation service on the first connection. Thus, for eachselected UE, before the reconfiguration, the first connection could beon the first carrier as a primary component carrier ofcarrier-aggregation and with the second carrier as one of one or moresecondary carriers for the carrier-aggregation service, and after thereconfiguration, the first connection could be on the second carrier asthe primary carrier of the carrier-aggregation service and the firstcarrier could be one of the one or more secondary carriers for thecarrier-aggregation service.

Yet further, as discussed above, for each selected UE, the act ofreconfiguring the UE's respective first connection could involvetransmitting from the first access node to the UE aconnection-reconfiguration message that directs reconfiguration of theUE's respective first connection to be on the second carrier instead ofon the first carrier.

Finally, FIG. 4 is a simplified block diagram of an example access node,which could be first access node 16 in FIG. 1, representing by way ofexample how a cellular system of FIG. 1, including the first access nodeand the second access node, could be configured to carry out variousdisclosed operations, including various features described above forinstance.

As shown in FIG. 4, the example access node includes a wirelesscommunication interface 54, a backhaul interface 56, and a controller58, all of which may be communicatively linked together by a system bus,network, or other connection mechanism 60 and/or could be integratedtogether or distributed in various ways.

In this example arrangement, the wireless communication interface 56could be configured to provide cellular coverage and to engage in airinterface communication with served UEs. As such, wireless communicationinterface 56 could comprise an antenna structure, which could be towermounted or could take other forms, and associated components such as apower amplifier and a wireless transceiver, to facilitate providing acoverage area on multiple carriers as shown in FIG. 1 and engaging intransmission and reception of control-plane and user-planecommunications in accordance with a RAT such as any of those notedabove. Further, backhaul interface 56 could comprise a wired or wirelessinterface, such as an Ethernet network communication interface,configured to support communication with other entities, such as withvarious core network entities and other access nodes for instance.

Controller 58 could then comprise control logic to cause the firstaccess node to carry out particular operations including those describedherein. As such, the controller 58 could take various forms, includingbut not limited to a processing unit including one or more processors(e.g., one or more general purpose microprocessors and/or one or morededicated processing units) and non-transitory data storage (e.g., oneor more volatile and/or non-volatile storage components, such asmagnetic, optical, or flash storage) holding program instructionsexecutable by the processing unit to cause the first access node tocarry out various operations described herein and thus to controloperation of the first access node.

It should also be understood that the present disclosure additionallycontemplates a non-transitory computer readable medium that stores, hasencoded thereon, or otherwise embodies program instructions executableto carry out such operations as well.

With this or other arrangements, the cellular system could thus beconfigured to serve multiple UEs with dual connectivity, where each UEis served concurrently by the first access node on a respective firstconnection according to a first RAT and by the second access node on arespective second connection according to a second RAT, and where all ofthe UE's respective first connections have a first carrier as anchorcarrier for the dual connectivity.

Further, the cellular system could be configured to detect, during theserving, that load on the first carrier is at least predefined thresholdhigh. And the cellular system could be configured to respond to thedetecting by (i) selecting one or more of the UEs based on each of theselected one or more UEs being within uplink range of the first accessnode on a second carrier higher in frequency than the first carrier and(ii) for each selected UE, reconfiguring the UE's respective firstconnection from having the first carrier as the anchor carrier for thedual connectivity to instead having the second carrier as the anchorcarrier for dual connectivity.

Exemplary embodiments have been described above. Those skilled in theart will understand, however, that changes and modifications may be madeto these embodiments without departing from the true scope and spirit ofthe invention.

We claim:
 1. A method for controlling dual connectivity, the methodcomprising: serving, by a cellular system, a plurality of user equipmentdevices (UEs) with dual connectivity, wherein each UE is servedconcurrently by a first access node on a respective first connectionaccording to a first radio access technology (RAT) and by a secondaccess node on a respective second connection according to a second RAT,wherein all of the UE's respective first connections have a firstcarrier as anchor carrier for the dual connectivity; during the serving,detecting, by the first access node, that load on the first carrier isat least predefined threshold high; and responsive to the detecting, (i)selecting, by the first access node, one or more of the UEs based oneach of the selected one or more UEs being within uplink range of thefirst access node on a second carrier higher in frequency than the firstcarrier and (ii) for each selected UE, reconfiguring the UE's respectivefirst connection from having the first carrier as the anchor carrier forthe dual connectivity to instead having the second carrier as the anchorcarrier for dual connectivity.
 2. The method of claim 1, wherein thefirst carrier defines a plurality of physical resource blocks (PRBs) perunit time, and wherein detecting that the load on the first carrier ispredefined threshold high comprises detecting that a rate of allocationof the PRBs is at least predefined threshold high.
 3. The method ofclaim 1, wherein the first carrier is defined in a first frequency band,wherein the second carrier is defined in a second frequency band, andwherein the first frequency band is lower than the second frequencyband.
 4. The method of claim 3, wherein the first frequency band is B25and wherein the second frequency band is B41.
 5. The method of claim 1,wherein selecting one or more of the UEs based on each of the selectedone or more UEs being within uplink range of the first access node onthe second carrier comprises: selecting the one or more UEs based ondetermining that a respective geographic location of each of theselected one or more UEs is within a predefined uplink geographic rangeof the first access node on the second carrier.
 6. The method of claim1, wherein selecting one or more of the UEs based on the selected one ormore UEs being within uplink range of the first access node on thesecond carrier comprises excluding, from the selecting, one or moreother of the UEs based on the one or more other UEs each not beingwithin predefined uplink geographic range of the first access node onthe second carrier.
 7. The method of claim 1, wherein for each selectedUE, before the reconfiguring, the first carrier is the only carrier inthe UE's respective first connection, and after the reconfiguring, thesecond carrier is the only carrier in the UE's respective firstconnection.
 8. The method of claim 1, wherein, for each selected UE,before the reconfiguring, the first carrier is a primary carrier forcarrier-aggregation service in the UE's respective first connection, andafter the reconfiguring, the second carrier is the primary carrier forthe carrier-aggregation service in the UE's respective first connection.9. The method of claim 8, wherein, for each selected UE, before thereconfiguring, the second carrier is one of one or more secondarycarriers for the carrier-aggregation service in the UE's respectivefirst connection, wherein the reconfiguring comprises making the secondcarrier the primary carrier for the carrier-aggregation service andmaking the first carrier one of the one or more secondary carriers forthe carrier-aggregation service.
 10. The method of claim 1, wherein, foreach selected UE, the reconfiguring comprises transmitting from thefirst access node to the UE a connection-reconfiguration message thatdirects reconfiguration of the UE's respective first connection to be onthe second carrier instead of on the first carrier.
 11. A cellularsystem comprising: a first access node; and a second access node,wherein the cellular system is configured to serve a plurality of userequipment devices (UEs) with dual connectivity, wherein each UE isserved concurrently by the first access node on a respective firstconnection according to a first radio access technology (RAT) and by thesecond access node on a respective second connection according to asecond RAT, wherein all of the UE's respective first connections have afirst carrier as anchor carrier for the dual connectivity, wherein thecellular system is configured to detect, during the serving, that loadon the first carrier is at least predefined threshold high, and whereinthe cellular system is configured to respond to the detecting by (i)selecting one or more of the UEs based on each of the selected one ormore UEs being within uplink range of the first access node on a secondcarrier higher in frequency than the first carrier and (ii) for eachselected UE, reconfiguring the UE's respective first connection fromhaving the first carrier as the anchor carrier for the dual connectivityto instead having the second carrier as the anchor carrier for dualconnectivity.
 12. The cellular system of claim 11, wherein the firstaccess node is configured to carry out the detecting, selecting, andreconfiguring.
 13. The cellular system of claim 11, wherein the firstcarrier defines a plurality of physical resource blocks (PRBs) per unittime, and wherein detecting that the load on the first carrier ispredefined threshold high comprises detecting that a rate of allocationof the PRBs is at least predefined threshold high.
 14. The cellularsystem of claim 11, wherein the first carrier is defined in a firstfrequency band, wherein the second carrier is defined in a secondfrequency band, and wherein the first frequency band is lower than thesecond frequency band.
 15. The cellular system of claim 11, whereinselecting one or more of the UEs based on each of the selected one ormore UEs being within uplink range of the first access node on thesecond carrier comprises: selecting the one or more UEs based ondetermining that a respective geographic location of each of theselected one or more UEs is within a predefined uplink geographic rangeof the first access node on the second carrier.
 16. The cellular systemof claim 11, wherein selecting one or more of the UEs based on theselected one or more UEs being within uplink range of the first accessnode on the second carrier comprises excluding, from the selecting, oneor more other of the UEs based on the one or more other UEs each notbeing within the predefined uplink geographic range of the first accessnode on the second carrier.
 17. The cellular system of claim 11, whereinfor each selected UE, before the reconfiguring, the first carrier is theonly carrier in the UE's respective first connection, and after thereconfiguring, the second carrier is the only carrier in the UE'srespective first connection.
 18. The cellular system of claim 11,wherein, for each selected UE, before the reconfiguring, the firstcarrier is a primary carrier for carrier-aggregation service in the UE'srespective first connection, and after the reconfiguring, the secondcarrier is the primary carrier for the carrier-aggregation service inthe UE's respective first connection.
 19. The cellular system of claim18, wherein, for each selected UE, before the reconfiguring, the secondcarrier is one of one or more secondary carriers for thecarrier-aggregation service in the UE's respective first connection,wherein the reconfiguring comprises making the second carrier theprimary carrier for the carrier-aggregation service and making the firstcarrier one of the one or more secondary carriers for thecarrier-aggregation service.
 20. The cellular system of claim 11,wherein, for each selected UE, the reconfiguring comprises transmittingfrom the first access node to the UE a connection-reconfigurationmessage that directs reconfiguration of the UE's respective firstconnection to be on the second carrier instead of on the first carrier.